Flexible polymer-based material for hot isostatic pressing or warm isostatic pressing molds

ABSTRACT

There is disclosed a sealable, flexible membrane for encapsulating a part to be isostatically pressed at an elevated temperature. The membrane includes at least one first layer of polymeric film having a melting point above the elevated temperature, and at least one second layer disposed on the first layer. The second layer comprising a metal. In one embodiment, the metal comes into contact with the part to be isostatically pressed. The membrane, which typically has a thickness ranging from 10 to about 500 μm, and is impermeable to the flow of liquids and gases when sealed, can be used to warm press parts up to about 350° C. and pressures ranging from 5,000 psi to 100,000 psi. Methods to isostatically press parts using this sealable, flexible membrane are also disclosed. Bags made from the sealable, flexible membrane that are used in isostatic presses are also disclosed.

This application claims the benefit of U.S. Provisional Application No.62/093,033, filed Dec. 17, 2014, which is incorporated herein byreference in its entirety.

The present disclosure generally relates to a polymer based membranesused to encapsulate parts prior to being isostatically pressed,typically at elevated temperatures. Methods of isostatically pressingparts at elevated temperatures by encapsulating them is the disclosedpolymer-based membrane are also disclosed.

Isostatic pressing is a powder processing technique that uses fluid orgas pressure in order to compact a part. In this process, metal orceramic powders are typically placed in a flexible container that servesas the mold for the pressed part. The flexible mold, which is commonlypolyurethane, can be removed and refilled after each pressure cycle(called wet bag) or can be an integral and permanent part of thepressing vessel (called dry bag). The wet bag process is typically usedfor larger, more complicated parts, whereas the dry bag method istypically used for compaction of simpler and smaller parts. Thismanufacturing process consists of two main categories, cold isostaticpressing and hot isostatic pressing.

Cold isostatic pressing, (CIP), is performed at room temperature anduses a mold made from an elastomer material such as urethane, rubber, orpolyvinyl chloride. One disadvantage to this manufacturing process isthe inability to achieve 100% density, and a low geometric accuracybecause of the flexible mold.

Hot isostatic pressing, (HIP), is performed at an elevated temperature,usually >75% of the melting point of the material to be processed, andthus causes an elimination of practically all porosity, producing apressed product that is essentially 100% dense. In addition to theelimination of porosity, this powder process provides nearly completebonding throughout the structure of the material. The mold material inhot isostatic pressing must be one that maintains its integritythroughout the operation, such as sheet metal, glass or ceramic. UnlikeCIP, molds used in HIP processes are not flexible at low temperaturesbut become “plastic” or deformable at higher temperatures.

Warm isostatic pressing, (WIP), is a process that falls between CIP andHIP conditions. It is performed at a temperature ranging from above roomtemperature to less than about 500° C. such as less than about 300° C.Warm isostatic pressing achieves some benefits of both cold isostaticpressing and hot isostatic pressing. In particular, warm isostaticpressing allows the use of a flexible mold, but the elevatedtemperatures associated with this process cause the resulting product toexhibit higher density than a CIP process. However, at temperaturesassociated with WIP, most metal cans used as molds in HIP processesretain a majority of their strength and thus resist the pressure beingtransmitted. Therefore, rather than deforming uniformly, these cans willbuckle and deform unevenly destroying or distorting the component thatis being fabricated.

In addition, rubber molds used for CIPing degrade at temperaturesassociated with WIPing. These rubber molds are also costly, and have alimited life. Furthermore, these rubber molds by virtue of the way theyare sealed for CIPing do not seal against the high pressure gas, and arepermeable to the pressurizing gases. Additionally, rubber molds tend tobe relatively thick (such as >5 mm thick) and have an elastic hysteresison decompression. This delay in recovering the original shape canactually cause damage for thin or fragile parts. Thus, rubber molds usedin CIP processes are impractical to use in combination; at the highertemperatures used in WIPing and use of gas pressure as a medium.

There remains a need for a mold material that can withstand the elevatedtemperatures of warm isostatic pressing, while not suffering from thepreviously noted deficiencies of current molds used in HIP and CIPprocesses.

There is disclosed a sealable membrane for encapsulating a part to beisostatically pressed at an elevated temperature, which is above roomtemperature, the membrane comprising: at least one first layer ofpolymeric film having a melting point above said elevated temperature:at least one second layer disposed on said first layer, the second layercomprising a metal interface that comes into contact with the part to beisostatically pressed. The membrane described herein has a thicknessranging from 10 to about 500 μm, and is impermeable to the flow ofliquids and gases when sealed.

There is also disclosed a method of isostatically pressing a part atelevated temperature, the method comprising: placing the part in asealable membrane comprising: at least one first layer of polymeric filmhaving a melting point above the elevated temperature; at least onesecond layer disposed on the first layer, the second layer comprising ametal that comes into contact with the part to be isostatically pressed,wherein the membrane has a thickness ranging from 10 to about 500 μm,sealing the membrane to form a hermetically sealed first bag that isimpermeable to the flow of liquids and gases; introducing thehermetically sealed first bag into an isostatic press; and applyingpressure to the hermetically sealed first bag at a temperature of up to350° C. via a pressurizing gas.

There is further disclosed a bag for encapsulating a part to beisostatically pressed at an elevated temperature, which is above roomtemperature, the bag comprising: at least one first layer of polymericfilm having a melting point above the elevated temperature; at least onesecond layer disposed on the first layer, the second layer comprising ametal that comes into contact with the part to be isostatically pressed,wherein the bag comprises at least one sealable, open end for receivingthe part to be pressed, wherein the at least one sealable, open endterms a hermetic seal that is impermeable to the flow of liquids andgases when sealed.

The present disclosure describes polymer-based membranes, such as a bagor pouch for encapsulating a part that is to be isostatically pressed atan elevated temperature, such as hot or warm isostatic pressing.

In some aspects, a sealable membrane for encapsulating a part to beisostatically pressed at an elevated temperature, which is above roomtemperature, comprises at least one first layer of polymeric film havinga melting point above the elevated temperature, and at least one secondlayer disposed on the first layer, the second layer comprising a metalthat comes into contact with the part to be isostatically pressed.

The disclosed membrane may have a thickness ranging from 10 to about 500μm, such as from 25 to 400 μm, from 50 to 300 μm, and from 100 to 200μm. The combination of material and thickness leads to a finished bag orpouch that can be hermetically sealed, and that is impermeable to theflow of liquids and gases. In one embodiment, the disclosed membrane hasno elastic hysteresis on decompression.

The polymer-based membrane includes any known polymer resin that canwithstand a temperature of up to 350° C., such as a temperature rangingfrom 30° C. to 350° C., or from 100° C. to 350° C., without thermaldegradation.

Non-limiting examples of such a polymer resin include polyethylene,polypropylene, such as oriented polypropylene, polyester, polyethyleneterephthalate (PET), such as biaxially-oriented PET, polyamide, orcombinations thereof.

In one embodiment, the polyethylene described herein may includeultrahigh molecular weight polyethylene.

In one embodiment, the polyamide may include copolyamides 6/12,copolyamides of polyamide 6 and a partially aromatic polyamide andternary copolyamides based on polyamide 6, polyamide 11, and polyamide66, or combinations thereof.

The second layer may comprise a metal that may be deposited using aphysical vapor deposition process thickness ranging from 0.1 to 2.0 μmusing. Examples of metals that can be used in the second layer includealuminum, copper and nickel.

In one embodiment, the second layer may comprise a metallized polymerfilm, such as metallized polyester films having a low coefficient offriction, such as one below 0.5 μs, below 0.4 μs, below 0.3 μs, such asa coefficient of friction ranging from 0.3 μs to 0.5 μs, (as measured byASTM 1894). No-limiting examples of such materials are those sold byToray™, under the tradename LumLife MS26 Lumirror® Polyester Films. Inone embodiment, the second layer comprising the metal or metallizedpolymer film comes into contact with the part to be isostaticallypressed.

The membrane described herein may comprise a laminate of two or morelayers, such as a laminate of multilayer thermoplastic films, oradditional layers of thermoplastic films. Non-limiting examples of theadditional layers of thermoplastic films that might be part of themembrane include comprise one or more layers chosen from a heat-sealablelayer, a gas barrier layer, an anti-sticking layer, or a strengtheninglayer.

In one embodiment, the anti-sticking layer comprises apolytetrafluoroethylene containing interlayer, such as DuPont's Teflon®brand.

In one embodiment, the disclosed membrane may further include athermoplastic polymeric adhesive in between the at least one first layerand at least one second layer, such as a layer located between alaminate of two or more layers.

In one embodiment, the disclosed membrane comprises a multilayerstructure of at least four layers comprising repeating layers of polymerfilm and metal or metallized film, wherein the resulting multilayer. Theresulting membrane may be impervious to aqueous solutions, both acidicand basic in chemical composition.

The present disclosure also describes methods of hot or warm isostaticpressing that includes encapsulating a part that is to be isostaticallypressed in the polymer-based membrane described herein.

In some aspects, the method of isostatically pressing a part at elevatedtemperature comprises: placing the part in at least one sealablemembrane comprising: at least one first layer of polymeric film having amelting point above the elevated temperature; at least one second layerdisposed on the first layer, the second layer comprising a metal thatcomes into contact with the part to be isostatically pressed.

The method next comprises sealing the membrane, which may have athickness ranging from 10 to about 500 μm, such as from 25 to 400 μm,from 50 to 300 μm, and from 100 to 200 μm, to form a hermetic seal thatis impermeable to the flow of liquids and gases.

After sealing the membrane, the hermetically sealed membrane is thenintroduced into the isostatic press, and pressure, which may range from5,000 psi to 100,000 psi, such as from 10,000 psi to 20,000 psi, isapplied to the part at a temperature of up to 350° C., such as atemperature ranging from 30° C. to 350° C., or from 100° C. to 350° C.,via a pressurizing gas, such as a argon or another inert gas.

The at least one first layer of polymeric film that can be used in thedisclosed methods include polyethylene, polypropylene, such as orientedpolypropylene, polyester, polyethylene terephthalate (PET), such asbiaxially-oriented PET, polyamide, or combinations thereof.

In one embodiment, the polyethylene described herein may includeultrahigh molecular weight polyethylene.

In one embodiment, the polyamide may include copolyamides 6/12,copolyamides of polyamide 6 and a partially aromatic polyamide andternary copolyamides based on polyamide 6, polyamide 11, and polyamide66, or combinations thereof.

The second layer used in the described method comprises a metal that maybe deposited using a physical vapor deposition process thickness rangingfrom 0.1 to 2.0 μm using. Non-limiting examples of such metals includealuminum, copper and nickel.

The method may also include depositing a layer of thermoplasticpolymeric adhesive in between the at least one first layer and at leastone second layer.

In one embodiment the method includes evacuated the membrane via atleast one port prior to applying said pressure. The membrane may be inthe form of a bag or a pouch that has one opening, or port that allowsit to be evacuated.

Multiple membranes may be used one over the other to provide aredundancy in the event the primary bag fails. For example, two, threeor even four bags may be used to insure desired sealing, and reduceissues associated with the permeability of gas through the bag.

Exemplary objects and advantages will be set forth in part in thedescription which follows, or may be learned by practice of theexemplary embodiments. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the invention, asclaimed.

The features and advantages of the present invention maybe more fullyshown by the following examples, which are provided for purposes ofillustration, and are not to be construed as limiting the invention inany way.

The part to be HIPed or WIPed is sized, and two sheets of the disclosedpolymer film are cut to be larger than the component. One layer isplaced on top of the other, which is followed by a heat sealing step ofthree (3) sides of the stacked film to create a pocket or envelope thatwill allow the part to easily slide into it. Alternatively a pre-madebag or tube of lay-flat tube can be used to create bag.

The part can then be inspected to determine if there are any sharp edgesthat may puncture the bag during processing. If there are sharp edges,they are preferentially rounded off or alternatively covered with a softtape or rubber over the edges to prevent bag damage.

In an embodiment, fixtures or pads can be custom made to preventpuncturing of the polymer film.

Bag sealer temperature and time are then set to ensure the film issealed and the layers of polymer fuse together creating a good seal.This is typically predetermined depending bag material and thickness.

Additionally, aluminum foil can be used to prevent sticking of the partto the film and will also provide some barrier to sharp edges of thecomponent. This aluminum foil, which can be used as an interlayerbetween the part that is being pressed and the heat sealable polymerfilm, is meant to eliminate or mitigate sticking of the part/powder tothe polyester film, such as DuPont's Mylar™ film. However, low tearstrength or ductility associated with some Al foils may require the useof a multiple-layer metalized film.

In one embodiment, the metallized material may comprise metallizedpolyester films, such as the metallized films sold by Toray, IncludingLumlife MS26 Lumirror® Polyester Films. These films have a mirrorsurface finish with a very low coefficient of friction, such as onebelow 0.5 μ_(s), below 0.4 μ_(s), below 0.3 μ_(s), such as a coefficientof friction ranging from 0.3 μ_(s) to 0.5 μ_(s), (as measured by ASTM1894). In one embodiment, the metallized material comes into contactwith said part to be isostatically pressed. As a result, this layershould not stick to the pressed part. In one embodiment, the metallizedmaterials are multilayer structures, such as one comprising a layer ofmetal, such as Al, Cu or Ni, that is deposited, such as vacuumdeposited, on a PET layer, with one or more optional layersthere-between. For example, these optional layers may comprise anadhesion assistant layer or an adhesion primer layer.

In one embodiment, a vacuum bag sealer is used to evacuate the bagaccording to desired conditions. For example, larger components willneed more time or in humid conditions more time is needed to degas thespace in the bag. Vacuum bag sealers can be used that ensure the latteris capable of effective sealing of higher temperature film, such asMylar™.

After sealing, the bag is again inspected to ensure it can hold avacuum, as evident by the bag remaining tightly contoured to the partrather than in a relax condition. The later suggest that a bag hasleaked or failed to seal properly.

Once satisfied that the bag is hermetically sealed, an oversized bag ismade in which the first hermetically sealed bag can be inserted. Againthe oversized second bag is vacuumed seal over the first bag. This is arecommended redundancy in the event the primary bag falls. This step canbe repeated 2, 3, 4 or more times if further insurance of sealing isrequired to insure a proper seal, and reduce permeability of gas duringprocessing. The sealed part or component can be then processed in theHIP or WIP system as described herein.

Unless otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present disclosure.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theembodiments disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope of theinvention being indicated by the following claims.

What is claimed is:
 1. A sealable membrane for encapsulating a part tobe isostatically pressed at a temperature up to 350° C., said membranecomprising: at least one first layer of polymeric film having a meltingpoint above 350° C.; at least one second layer disposed on said firstlayer, said second layer comprising a metal, wherein said membrane has athickness ranging from 10 to about 500 μm, is impermeable to the flow ofliquids and gases when sealed and can withstand a temperature of 350° C.without thermal degradation.
 2. The membrane of claim 1, wherein said atleast one first layer of polymeric film comprises polyethylene,polyester, polyethylene terephthalate (PET), polyamide, or combinationsthereof.
 3. The membrane of claim 2, wherein said at least one firstlayer of polymeric film comprises one or more of the following:polyethylene comprising ultrahigh molecular weight polyethylene;polyamide chosen from copolyamides 6/12, copolyamides of polyamide 6 anda partially aromatic polyamide and ternary copolyamides based onpolyamide 6, polyamide 11, and polyamide 66, or combinations thereof;and PET that is biaxially oriented.
 4. The membrane of claim 1, whereinsaid metal comprises aluminum, copper, or nickel.
 5. The membrane ofclaim 1, wherein the second layer comes into contact with said part tobe isostatically pressed, and comprises a multilayer, metallizedmaterial.
 6. The membrane of claim 5, wherein the multilayer, metallizedmaterial comprises a polyester film layer coated with an aluminum layer.7. The membrane of claim 5, wherein the multilayer, metallized materialhas a coefficient of friction below 0.5 μs.
 8. The membrane of claim 1,further comprising a layer of thermoplastic polymeric adhesive inbetween the at least one first layer and at least one second layer. 9.The membrane of claim 1, wherein said membrane has a thickness rangingfrom 20 to 100 μm.
 10. The membrane of claim 1, wherein said membranecomprises a multilayer structure of at least four layers, said fourlayers comprising repeating layers of polymer film and metal ormetallized film.
 11. The membrane of claim 10, wherein the multilayerstructure is impervious to aqueous solutions, both acidic and basic. 12.A bag comprising the membrane of claim 1, wherein said bag has at leastone opening for placing a part to be pressed therein, said at least oneopening having at least one seal that hermetically seals the bag, andoptionally a port to allow the bag to be evacuated.
 13. The membrane ofclaim 1, wherein said at least one first layer comprises a laminate ofadditional thermoplastic films, said additional thermoplastic filmschosen from a heat-sealable layer, a gas barrier layer, an anti-sticklayer, or a strengthening layer.
 14. The membrane of claim 13, whereinsaid gas barrier layer has an oxygen transmission rate there-throughranging from 0 to 5 cm³/100 in²/24 hours.
 15. The membrane of claim 13,wherein the anti-stick layer comprises a polytetrafluoroethylenecontaining material.
 16. A bag for encapsulating a part to beisostatically pressed at a temperature up to 350° C., said bagcomprising: at least one first layer of polymeric film having a meltingpoint above 350° C.; at least one second layer disposed on said firstlayer, said second layer comprising a metal, wherein said bag canwithstand a temperature of 350° C. without thermal degradation andcomprises at least one sealable, open end for receiving the part to bepressed, wherein said at least one sealable, open end forms a hermeticseal that is impermeable to the flow of liquids and gases when sealed.